1. Technical Field
The present application relates to a system and method for adjusting warpage of a wafer through gradual heating and cooling.
2. Description of the Related Art
Currently hundreds of copies of the same semiconductor die are formed on a large silicon wafer and then cut apart as individual for use in electronic devices.
Once the chips are cut from the silicon wafer, they are not yet ready for use. The chips must be packaged in a way that not only provides physical protection from external environmental factors, but also to couple the chips to electrical connections used to connect to other electronic devices. Due to the very small size of the chip's components and electrical connections, it is preferable to develop methods of creating the chip packages that keep efficiency of production up and cost down.
One technique in use today is to place the individual die on a new substrate spaced some distance apart from each other. This new substrate may be round, square or any desired shape and made form any desired material that will support individual die. The new substrate having a large number of die placed thereon spaced apart from each other is called a reconstituted wafer, also referred to as an EWLB wafer in the industry. After the die are placed on the new substrate to form the reconstituted wafer, further processing takes place to electrically connect the die to terminals, solder balls or other electrical connections.
As part of forming the reconstitution wafer, a molding compound is flowed over and around the die to enclose them and the electrical lead. Due to the molding layer and the die being of very different materials, however, undesirable stresses may occur near where the molding layer and the die make contact. In some instances, the EWLB wafer may crack, the molding layer or the die may fracture, or other breaks may occur which would result in a semiconductor chip that does not work. Another effect due to the difference in materials between the molding layer and the chip is that the molding layer may cause the reconstituted wafer to become warped or deformed. While there may be no fractures in the chips or molding layer, a warped or deformed reconstituted wafer may also be undesirable and lead to degraded performance of the embedded chips.